[Amps] RF coupling to 8877 filaments?

[Ron Youvan]

Mike McCarthy, W1NR wrote:

> I am in the process of building an 8877 amp and through the course of
> comparing various designs I came across one in Orr's Handbook where the
> input RF was coupled to the filaments with .01 capacitors. This, of
> course, adds an RF choke to the filament leads and is not done in most
> other designs I have looked at.

> I think the article mentions this is to prevent or minimize RF heating
> of the filaments. Is this a valid reason? Are there some other reasons
> to do this?

> I am seriously considering NOT implementing it and going with the Kiss
> approach. Opinions?

   I think filament chokes are used with cathode driven amplifiers only.  I have never heard of 
using them with grid driven amplifiers.  The only alternate that I have ever heard of is threading 
one conductor inside of another and tuning the "coil."
I don't understand any specific connection between the capacitors and RF choke/s.
-- 
    73 Ron KA4INM - All E-mail sent to this address shall linger in the Google cloud forever!